A so-called venetian blind includes a plurality of slats which can be adjusted to various angles for controlling the amount of light passing therethrough and also may be raised or lowered to any desired height. A further well accepted form of window covering unit possessing some similarities to a conventional venetian blind, is a window covering consisting of a pleated fabric which can be raised or lowered to any desired height by cords extending through apertures in a pleated fabric. In both of these window covering units, adjustment of the cords to produce the desired height is typically accomplished by manipulation of the amount of cord which extends outwardly from the window covering and, more particularly, extends downwardly from a headrail located at the top of the window covering.
A highly desirable feature is that the cord used for positioning the height of the window covering or blind remains fixedly located after each adjustment. The very earliest approach to a solution for this problem was to provide a peg or stanchion about which the cord was tied. More recently, mechanical cord locks have been developed including pins between which the cords must pass and which pins accomplish a controlled amount of clamping force onto the cord at the conclusion of each height adjustment. Such cord locks, in the past have been subject to various deficiencies making them less than completely satisfactory in operation. For example, in certain prior cord locks, the specific means for obtaining the necessary cord force tended to induce substantial wear on a cord causing it to become frayed and eventually to break necessitating replacement. In certain other cord locks, the mechanical advantage of the various parts used to clamp the cord into a fixed position is insufficient making the cord lock unsteady and unreliable, in subjecting the cord lock device to the possibility of becoming disengaged allowing the blind to slip to some lower position. In still other types of known cord locks, the members that achieve the clamping of the cord tend, during use, to become burnished reducing the frictional engagement of the cord and allowing it to slip through with obvious undesirable results.